1) Field of the Disclosure
The disclosure relates to coatings for composites. In particular, the disclosure relates to fully dense barrier-coating systems and methods for composites.
2) Description of Related Art
Polymer-matrix composites (PMCs), such as high-temperature polymer-matrix composites (HTPMCs), are typically used in the aircraft and aerospace industry for the weight reductions they offer when used to replace metal components. However, exposure to high-temperatures (e.g., 350 degrees Fahrenheit to 700 degrees Fahrenheit) can reduce the mechanical properties of the PMCs and HTPMCs and can cause oxidative degradation of the PMCs and HTPMCs. For example, HTPMCs typically have limited lifetimes of approximately between 1000 hours and 3000 hours at such elevated temperatures, primarily due to oxidation reactions, which reactions severely degrade the HTPMCs. In an attempt to extend the lifetime of such PMCs and HTPMCs, known barrier coatings or layers which prevent, reduce, or inhibit the permeation of a selected substrate with a gas, vapor, chemical, and/or aroma have been developed for use with PMCs and HTPMCs. For example, known ceramic-based barrier coatings have been used with PMCs and HTPMCs. However, such known ceramic-based barrier coatings do not prevent thermo-oxidative degradation, do not prevent oxygen diffusion, and, if exposure times are sufficiently long, do not adequately reduce temperature. Moreover, such known ceramic-based barrier coatings have not demonstrated desired ranges of durability in high-flow airstreams, such as encountered in exhaust-washed aircraft structures. In addition, such known ceramic-based barrier coatings have coefficients of thermal expansion (CTEs) that are sufficiently different from PMCs and HTPMCs and can cause strain mismatch between the ceramic-based barrier coating and the PMC or HTPMC substrate that can cause the coating to crack or spall, thereby exposing the substrate to the environment, thus resulting in degradation of the PMC or HTPMC.
In addition, known oxygen-barrier coatings exist for use with PMCs and HTPMCs. However, such known oxygen-barrier coatings cannot withstand use at elevated temperatures in the 350-degree Fahrenheit to 700-degree Fahrenheit range for extended periods without cracking, spalling, debonding, and/or eroding.
In addition, known metal-based barrier coatings exist for use with PMCs and HTPMCs. However, such known metal-based coatings have coefficients of thermal expansion (CTEs) that are sufficiently different from PMCs and HTPMCs and can cause strain mismatch between the metal-based barrier coating and the PMC or HTPMC substrate, that can cause the coating to crack or spall, thereby exposing the substrate to the environment, thus resulting in degradation of the PMC or HTPMC.
Accordingly, there is a need for a dense barrier-coating system and method that provide advantages over known coatings and systems.